The use of fiber optics technology in data communication is rapidly expanding. Optic fiber transmission links are used widely in connecting computers, instrumentation, and telephones. Fiber optic systems have tremendous advantages over copper-conductor systems. Besides being smaller and lighter than copper-conductor systems, fiber optic systems offer total electrical isolation, extremely high-speed wideband capability, and complete immunity to both noise and the broad spectrum of interference. Most importantly, fiber optics communication links are much less expensive than the copper-conductor systems.
With this rapid expansion of fiber optics technology, there is an increased demand for higher transmission rates and increased bandwidth. However, as all light pulses are unipolar, certain difficulties arise in the high-speed transmission of a long stream of ONES or ZEROS. In order to transmit such long streams, various coding schemes are utilized to reduce the distortion. Various coding and modulation schemes have been developed such as Manchester coding, frequency shift coding, phase shift coding, as well as various other coding schemes developed from these codes.
Additionally, the data to be transmitted through such systems occurs in several formats, such as asynchronous, synchronous, or bisynchronous. The data rates in these formats very widely, with the asynchronous data typically being at a much lower rate than the synchronous data. Accordingly, modern fiber optic transmisson systems should be able to transmit both asynchronous or synchronous data, and also to code such data in a manner preventing any distortion or loss of information.
Several fiber optic transmitting and receiving circuits are currently manufactured, but all of them are either limited in capability, or very expensive. The circuits currently available operate only in the asynchronous or the synchronous mode, and at limited data speeds. Furthermore, for the transmission of synchronous data, the clock and the data synchronized to it are often transmitted separately. Also, those circuits utilizing the various coding schemes currently available are often quite complex, and therefore very expensive.
Most importantly, few of the units currently available provide any indication of the integrity of the optical communications link. That is, the systems simply transmit data. It is very important to have an indication of the link continuity independently of the presence of the data in order to insure that a valid data link exists.
Accordingly, it is the principal object of the present invention to transmit and receive digital data through a fiber optics cable in an inexpensive and efficient manner.
It is another object of the present invention to transmit and receive both synchronous and asynchronous data through a fiber optics cable with a simple circuit.
It is a further object of the present invention to transmit and receive asynchronous and synchronous data over a wide range of speeds.
It is still another object of the present invention to transmit and receive synchronous data without the necessity of separately transmitting and receiving the clock to which the data is synchronized.
It is an additional object of the present invention to transmit data into a fiber optics communications cable in a format which is both easy to encode and decode.
It is a final object of the present invention to provide an indication of the operationality or viability of a fiber optics communication link when no data is being transmitted over the link.